Hydrofoil lift



United States Patent 3,164,119 HYDRUFGIL LEFT Lucas I... lmrnannei, Newton Highiands, and R.

Woodward, flariisie, Mass, assignors to Qosrno i33 namics, lilo, Newton Upper Fails, Mass a corporation of Massachusetts Filed Mar. 26, 1963, No. 255,4i'2 l7 (Ziairns. (fit. 114-665) This invention relates to hydrofoil lifting devices and has for its principal objects to provide devices of different form embodying equivalent physical structure for use with aquatic structures and/ or amphibian craft to elevate and/ or to assist in elevating the structure or craft from the surface of the water either for sport or for utility; to provide a device which has a high degree of stability, enabling maintenance of height and affording resistance to upsetting response from wave disturbances and/or speed changes and, at the same time, affording a high degree of control both with respect to the elevation and flight; to provide a device which is highly maneuverable with a minimum of skill thus affording amusement for the amateur as well as the professional; to provide a device which is operative at relatively low speed so as to be available to the owner of boats of low power as well as those of high power and to suit the daring and/or skill of the participant and to make it easier to initiate flight; and to provide a device which can be applied to a pair of skis, a single slalom ski, aquaplanes, surfboards, saucers, boats, amphibious craft and aircraft.

As herein illustrated, the device comprises foil elements disposed transversely of the direction of movement in spaced parallel relation, and means for rigidly securing the foils in spaced parallel relation to the underside of the structure, with the foils situated forwardly and rearward- 1y of the center of the supported weight. The means securing the foils to the underside of the structure is a strut having diverging legs, the upper divergent ends of which are secured to the structure, transversely thereof. A boom, secured to the convergent ends of the legs at their intersections with its axis perpendicular to the plane of the legs, supports the foils, the foil forwardly of the legs being secured to the upper side of the boom and having a positive lift effect and the foil at the rear of the legs being secured to the underside of the boom and having a negative lift effect. The diverging legs of the strut provide lift and, in one form, limbs projecting toward each other to which are attached means for securing a ski to the upper end of each leg. Alternatively, the upper ends of the legs may be joined by a horizontal part towhich the ski fastening means may be secured, or by means of which any structure to be elevated thereby may be secured. In this form the horizontal part is also a foil and provides lift at low speed during emergence of the device from the water.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is a perspective of the hydrofoil device showing, in phantom, a pair of water skis attached thereto;

FIG. 2 is an elevation of the device as seen from the left-hand side of FIG. '1;

FIG. 3 is an elevation of a modification in which the divergent legs are joined at their upper ends;

FlG. 3a is a bottom view of part of the ski showing a scale marked thereon to facilitate attaching the device to the ski at the best position;

FIG. 4 is a fragmentary elevation of the upper part of the device showing a clamping bracket for a ski;

FIG. 5 is a fragmentary elevation of the device showing another form of clamping bracket for a ski;

FIG. '6 is a plan view. of FIG. 5;

3,164,119 Patented Jan. 5, 1965 FIG. 7 is a fragmentary elevation at the upper part of the strut showing another form of clamping bracket for a ski;

FIG. 8 is an elevation as seen from the left-hand side of FIG. 7;

FIG. 9 is a fragmentary elevation of still another form of clamp for a ski;

FIG. 10 is a perspective of the device adapted to be attached to a surfboard; and

FIG. 11 is an elevation diagrammatically showing the position of the foot and leg on the ski in relation to the device attached to the ski, showing the ski elevated from the surface of the water for low and high speed flight and illustrating the various forces involved.

Referring to the drawings, FIG. 1 shows the hydrofoil device It with a pair of water skis 12 attached there to, although it is to be understood that other aquatic structures may be attached thereto, for example a single slalom ski, a surfboard, a saucer, or the like, and that it may be employed in conjunction with boats, amphibious crafts and aircrafts, the purpose of the device in these latter instances being utilitarian rather than for sport to assist in lifting the craft from the water. I

The device comprises a V-shaped strut 14 having upwardly diverging legs 16-16, at the upper divergent ends of which are inwardly extending, horizontal limbs 18-18 to which skis or the like may be attached with their longitudinal axes perpendicular to the plane of the legs. The lower convergent ends of the legs lld-l6 are secured by means of welding or bolts to a horizontally disposed boom 20, with its axis extending forwardly and rearwardly of the plane of the legs and perpendicular thereto. Foils 22 and 24 are attached to the boom 20, forwardly and rearwardly of the strut and transversely of the boom, the forward foil 22 being attached to the upper side of the boom and having a positive lifting effect and the foil 24 being attached to the underside of the boom and having a negative lifting effect.

In an alternative form, the strut 14, as shown in FIG. 3, may be of delta-shape, having a horizontal part 26 joining the upper divergent extremities of the legs 16l6. The legs in each form and the horizontal part in the delta strut are of lenticular cross-section and constitute lifting foils.

The device may be modified for attachment, as shown in FIG. 10, to a surfboard 30 or similar structure by attaching the boom 2d to spaced struts Mir-14a. In similar manner, foils may be attached to theunderside of the hull of a boat or the pontoon of an aircraft. Addi-' tional lift may be attained by additional foils, below those shown, byextending the strut for this purpose.

A successfully operated embodiment of the invention which proved practical from the standpoint of manufacture and use, has an overall height, that is, from the upper ends of its divergent legs to the convergent lower ends of 23 inches and an overall width, between the upper ends of the divergent legs, of 22 inches. The legs have a foil cross-section lenticular in shape, situated with the fiat sides disposed outwardly and the convex sides disposed inwardly, which is 2.75 inches in width.

The foil 22., which constitutes the forward wing and provides the positive lifting effect, is 2.75 inches wide by 14 inches long, is fastened to the boom so that its leading edge is 6.75 inches from the forward edge of the strut and inclines to the horizontal. The foil 24; which constitutes the stabilizer, is 2.75 inches wide, 10 inches long, is mounted 10 inches behind the forward edge of the strut with its convex side facing downwardly and. having an incidence of 0. When employing the foregoing dimensions the'ski's are mounted 1.00 inch above the strut and the foot of the skier should be so such as to return the device to the original depth.

positioned that the ankle bone, which represents the approximate application of the weight of the skier, should be approximately 6 inches ahead of the front edge of The forces involved and their direction are di'agramath cally shown in FIG. 11 and, of c urse, exist in a state of equilibrium under normal controlled flight. The forces are designated in FIG. 11 by reference letters and the following table indicates their meaning:

Ds-Stabilizer drag Dsk-Ski drag, negligible when out of water Dv\/ drag Ls-Stabilizer lift, normally negative LskSki lift, negligible when out of water Lv-V lift LwWing lift M-Ankle moment, A.R. to balance all others MsStabilizer moment, normally negative Msk-Ski moment, negligible when out of Water MvV moment To-Operator thrust, equal to tow line tension Wf-Weight of foil assembly Wo-Operators weight Wsk-Ski Weight It is to be understood that the variables involved are so numerous and so dependent upon each other that, as a practical matter, it is impossible to place limits upon the proportions of the device andits use under operating conditions since extreme conditions of loading, that is, weight of the operator, low and high speed towing, wave con ditions and proportions of the foils will change the operation and require adjustment. Primarily, of course, the device must be of sufficient strength and rigidity to withstand the strain imposed on it by the combined effect of the Weight of the supporting structure and the person or persons occupying the structure, the force imparted to it by the tow line and the stresses developed by the turbulence of the waves.

In addition to the foregoing, it is important that the device provide flying stability. This is achieved by placing the legs of the strut sufiiciently aft of the forward foil or wing and of the operators feet, so that the entire device tends to stay behind or opposite the direction of pull. If the strut is too far forward, directional instability develops which results in uncontnolled deviation of, flight to the right or left. Too much directional stability on the other hand makes the device uncontrollable. For best results, with a V-shaped strut of the dimensions referred to above, the wings should be 6.75 inches ahead of the leading edge of the strut. The projected side areas of the legs have considerable effect on the directional stability; however, from the standpoint of directional stability alone, it is not important whether the strut is in the form of a V, as illustrated, or a single vertical member as shown in FIG. 10.

It is also desirable automatically to achieve height stability. Thus, for example, if there is a height disturbance, as the result of a wave, it is desirable that this disturbance be followed by an automatic corrective action Instability in this respect-tends to cause the device to either fiyout of the water or'plunge too deeply-either extreme demanding attention and skill on the. part of the participant. Height stability-is achieved by placing the strut as far forward as the directional stability limitations will permit. In this forward position and with the proper degree of foil incidence the strut becomes a lifting surface which supports roughly one'third of the total weight, the wing carrying the remaining two-thirds. Since the f-shaped strut pierces the surface, it loses its lifting capacity in approximate proportion to the height at any given time thus giving the desired degree of height stability.

Other factors such as the V-angle of the strut, foil incidence and foil twist influence the height stability characteristics.

Since the device flies in a "cry restricted height zone, the pitch stability is difilCUlt to distinguish from height stability. Pitch stability concerns the longitudinal attitude (ankle angle) and the pitching moment (ankle control moment) required to hold the device at the correct flying height. Even though designed to provide a proper positive static height stability, a negative longitudinal stability will result in an unstable height characteristic.

Longitudinal or pitch stability requires that the operators weight be forward of the aerodynamic center, that being the point about which the pitching moment is constant with the pitch angle. Thus the pitch longitudinal stability is adjusted by moving the entire device with respect to the ski foot harness. Such adjustment is afforded, as will appear hereinafter, by clamping attachmerits which make it easy to adjust the device relative to the skis and hence to obtain the optimum position for light and heavy participants.

From a roll standpoint, the device is analogous to a bicycle, because the center of gravity is far above the point of support. As in the case of the bicycle, the participant is confronted with no problem in staying on top by using steering control.

The particular success of the hydrofoil disclosed herein, from the standpoint of performance, such as high lift, low drag, etc, as well as stability and control, results essentially from the combination of a totally submerged forward foil or wing having a positive lift effect; a totally submerged rearward foil constituting a stabilizer of negative lift; and a V-chaped or delta-shaped strut partially submerged, positioned midway between the wing and stabilizer.

As previously pointed out, the V-shaped strut provides a positive lifting action. The horizontal member of the delta strut not only provides for a wide variety of attachment but is also designed to provide an additional lifting component which greatly assists in bringing the operator to the surface at slow speed.

The upper cross-member, whether bent from the leg of the V or made of separate pieces, is provided with a negative zero lift angle which makes it effective in lifting while the skis are at an attitude of +5" to +25". The wing is less effective in this range, contributing its greatest lift from the higher speed range where the skis are at an attitude of +l0 to l(). The lift of the cross-member is important for it greatly assists the novice skier or the low-powered boat owner to achieve ordinary ski operations at a lower speed.

The hydrofoil device may be supplied as a unit for attachment to skis or the like already in the possession of the purchaser of the device, or it may be supplied as part of a kit, consisting of the device and a pair of skis or other structure specially designed for use therewith, and provided With suitable attaching means.

One form of attaching means for a strut is shown in FIG. 4 in the form of a clamping bracket 32 comprising a ferrule 34 slidably disposed on the leg 16, a part 36, substantially parallel to the leg, a part 38 substantially perpendicular to the limb l8 and a part 40 supported by an elbow 42 parallel to the limb 18. The part 40 constitutes a clamping foot and may be adjusted vertically with respect to the limb 18 bysliding the ferrule 34 along the leg 16 so as to receive the outer edge of a ski S therebetween. an upward thrust on the foot 4% which cants the ferrule 34 with respect to the leg 1d so as to bind it in place. Two such brackets are employed, one at the upper end of each leg. Somewhat greater security may be obtained with clamping means such as shown in FIGS. 5 and 6. A bracket 44 is attached by suitable means to the leg 16 and has a horizontal flange 4d spaced from the top of the leg sufficiently to permit inserting the edge of the ski between the leg and the flange. A pair of straps 4848 are fastened to the flange at one end and have at their opposite ends hooks St) for engagement with the inner edge of the ski. The hooks 5d are secured to the straps by screws 52 or the like for shortening or pulling up the strap. A toggle or snap-lock assembly is considered to be the full equivalent.

Clamping means particularly suited for the delta-shaped strut (FIG. 3) is shown in FIGS. 7, 8 and 9. In PEG. 8 the means comprises brackets 54 and 56. The bracket 54 is fixed to the horizontal part 26 and the bracket 56 is perforated so as to be slidable therealong, both for the purpose of adjusting the distance between the two for skis of dilferent width and for the purpose of locking the parts in place as will appear. The upper extremity of each bracket 54, 56 has an outwardly extending, rightaugle, horizontal portion 58 and a vertical portion 60 for contact, respectively, with the bottom side of the ski and the edges of the ski. The brackets 54 and 56 contain slots 62 and flexible elements in the form of straps 64 are threaded through the slots so that they may be looped around the underside of the ski and over the top side for securement of their ends by means of clamps 66. It is necessary to provide some means to prevent the brackets 54 and 56 from sliding freely along the horizontal part 226 during flight. Tape, solder, weld, pins, screws, plastic cement, or other means are suitable for fixing the relative The weight of the skier on the ski exerts the strap tight one or both brackets may be caused to bite into the horizontal part 26, and thus lock the clamping assembly in place.

It is to be understood that while the several forms of clamping devices related above are considered to be particularly expedient for the purpose of attaching and detaching skis and for adjustment to different ski size, it is within the province of the invention to use any suitable means for attaching the ski thereto.

To assist in locating the device in the correct position during assembly for optimum performance, the bottom surfaces of the skis may be provided with scales C (FIG. 3a), longitudinally thereof, graduated to show the position for various specific weights.

The device described above has a single wing and stabi lizer assembly, however, it is within the scope of the invention to modify the lift afforded by this assembly by adding, for example, a second wing between the first wing and the strut, for the purpose of reducing the take-off speed and to assist in bringing about emergence of heavy operators and/ or by the use of low powered boats. To further increase the lift, two V-shaped struts may be used in place of the single strut shown, for example, in FIG. 10. It is also contemplated that several wing and stabilizer assemblies may be cascaded by extension of the strut so that the assemblies are arranged in spaced parallel relation and some, at least the upper ones of the assemblies, will be lifted completely out of the water in flight.

When attaching the device to other watercraft appropriate attaching means will be used for the particular installation. Advantages of the clamping brackets shown reside in the minimum use of screws, fittings and the like,

which increase drag and/or weight and the avoidance of loss of strength which would be incurred if the parts were welded, riveted or secured by other components which required piercing the strut, and to the fact that they are adjustable for any width of ski and/ or taper of ski and that by removing two of these brackets the remaining two may be used for securement to an aquaplane or a single slalom type ski.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. A hydrofoil lifting device for elevating an aquatic structure from the water when moved therealong comprising a totally submergedvwing foil having a positive lift eifect, a totally submerged stabilizing foil having a negative lift effect, a strut extending downwardly from the underside of the structure, and means rigidly secured to the lower end of the strut, said means extending forwardly and rearwardly thereof and said wing and stabilizer foils being secured transversely thereof in spaced parallel relation to each other with the wing ahead of the strut land the stabilizer behind the strut.

' 2. A hydrofoil lifting device for elevating an aquatic structure from the water when moving at a predetermined speed comprising a strut fixed to the underside of the structure having transversely disposed, downwardly converging legs located at a connected plane at their upper divergent ends to the structure, a boom secured to the convergent lower ends of the legs so as to extend forwardly and rearwardly with respect to the transverse structure from the water when moving at a predetermined speed comprising a V-shaped strut fixed to the underside of the structure-with the legs disposed transversely andwith the upper divergent ends of the legs connected to the structure, an elongate boom fixed to the lower converging ends of the legs at the apex of the V-shaped strut, and foils fixed tothe boom forwardly and rearwardly of the strut, parallel to each other and to the underside of the structure, the forward foil being secured to the upper side of the boom and having a positive lift elfectand the rearward foil being secured to the underside of the boom and having a negative lift effect.

4. A hydrofoil lifting device for elevating an aquatic structure from the water when moving at a predetermined speed comprising a V-shaped strut having diverging legs, a boom secured to the foot of the strut at the junction of the legs with its axis perpendicular to the plane of the legs, foils secured transversely of the boom forwardly and rearwardly of the legs, and means at the divergent upper ends of the legs for securing a body-supporting structure thereto.

5. A hydrofoil lifting device according to claim 4, wherein the legs constitute foils which have a lifting effect which supplements the lift afforded by the wing.

6. A hydrofoil lifting device according to claim 4, wherein the legs constitute foils and provide lift which supplement that of the wing and supports about one-third the total weight.

'7. A hydrofoil lifting device according to claim 4, wherein the legs constitute foils and provide added lift which decreases in proportion to the height of emergence from the water thus providing height stability.

8. A hydro-foil lifting device for elevating an aquatic structure from the water when moving at a predetermined speed comprising a V-shaped strut having diverging legs, a boom secured to the foot of the stint at the junction of the legs with its axis perpendicularto the plane of the legs, foils secured transversely of the boom forwardly and rearwardly of the legs, limbs at the upper'diverge'nt ends of the legs extending toward each other, and means on the limbs for detachably securing a body-supporting structure thereto. 7

9. A hydrofoil lifting device for elevating an aquatic structure from the water comprising a V -shaped strut having divergent legs, a boom secured to the foot of the strut at the junction of the legs with its axis perpendicular to the plane of the legs, foils secured transversely of the boom forwardly and rearwardly of the legs, limbs at the upper divergent ends of the legs extending toward each other, and attaching means on the limbs for detachably securing Water skis thereto in spaced parallel relation.

10. A hydrofoil lifting device for elevating an aquatic structure from the water when moving at'a predetermined speed comprising a delta-shaped strut having a horizontal part and downwardly converging legs, the upper divergent ends of the legsbeing connected to the opposite ends of the part, an elongate boom fixed to the convergent lower ends of the legs at their intersection with its axis perpendicular to the plane of the legs, foil-s fixed to the boom forwardly and rearwardly of the plane of the legs in spaced parallel relation to each other and to the horizontal part, and fastening means on the horizontal part for detachably securing a body-supporting structure thereto.

11. A hydrofoil lifting deviceaccording to claim 10, wherein the horizontal part constitutes a foil having a lifting effect supplementing that of the wing during emergence of the device from the water.

i 12'. A hydrofoil lifting device for attachment to a ski or a pair of skis to effect lifting of the skier to a position above the surface of the water when being towed at a predetermined speed, comprising a pair of foils and means to which a ski or a pair of skis areadapted to be attached for supporting the foils spaced below the ski or pair of skis in parallel relation thereto, with the foils spaced lengthwise of the ski'orpair of skis forwardly and rearwardly of the place of attachment of the ski or pair of skis to said means, and with the forward foil located substantially vertically below the center of weight of the skier.

13. A hydrofoil lifting device according to claim 12, wherein the attaching means comprises clamps, each having a ferrule slidably supported on the leg of the strut, a part attached to the ferrule substantially perpendicular thereto and parallel to the leg, and a second part supported at the upper end of the one part in substantially parallel relation to the limb at the upper end of the leg, said second part and limb being adapted to receive the outer edge of a ski and to clamp the ski to the leg by jamming of the ferrule against the leg.

14. A hydrofoil lifting device according to claim 12, wherein the attaching means comprises clamps, each having a ferrule slidable on a leg of the strut, a first part fixed to the ferrule substantially parallel to the leg, a second part fixed to the first part substantially perpendicular to the limb, and a third part substantially parallel to the limb fixed to the second part, said second part being adapted to have engagement with the edge of the ski and the third part and limb being adapted to have engagement with the top and bottom surfaces of the ski adjacent the edge.

15. A hydrofoil lifting device according to claim 12, wherein the attaching means comprises a pair of transversely spaced bracket elements, each having a leg supported by the horizontal part, oppositely extending rightangle supports at the upper ends of the legs which collectively provide support for the bottom side and opposite edges of a ski placed between them, said legs containing slots, elongate flexible elements threaded through the slots, and means for securing the ends of the elements about the ski.

16. A hydrofoil apparatus according to claim 15, wherein one of the brackets is fixed to the horizontal part and the other is slidable thereon.

17. A hydrofoil apparatus according to claim 15, wherein both of the brackets are slidable along the horizontal part and are adapted to be fixed relative thereto by constriction of the flexible element.

References Cited in the file of this patent UNITED STATES PATENTS 1,252,781 Clark Jan. 8, 1918 2,121,432 Jacobson June 21, 1938 2,459,953 Mills Ian. 25, 1949 2,751,612 Shepard June 26, 1956 2,930,338 Flomenhoft Mar. 29, 1960 2,944,413 Black July 12, 1960 2,983,413 Verwers May 9, 1961 3,013,515 More] Dec. 19, 1961 3,094,960 Lang June 25, 1963 FOREIGN PATENTS 149,606 Switzerland Nov. 16, 1931 1,001,146 Germany Jan. 17, 1957 

1. A HYDROFOIL LIFTING DEVICE FOR ELEVATING AN AQUATIC STRUCTURE FROM THE WATER WHEN MOVED THEREALONG COMPRISING A TOTALLY SUBMERGED WING FOIL HAVING A POSITIVE LIFT EFFECT, A TOTALLY SUBMERGED STABILIZING FOIL HAVING A NEGATIVE LIFT EFFECT, A STRUT EXTENDING DOWNWARDLY FROM THE UNDERSIDE OF THE STRUCTURE, AND MEANS RIGIDLY SECURED TO THE LOWER END OF THE STRUT, SAID MEANS EXTENDING FORWARDLY AND REARWARDLY THEREOF AND SAID WING AND STABILIZER FOILS BEING SECURED TRANSVERSELY THEREOF IN SPACED PARALLEL RELATION TO EACH OTHER WITH THE WING AHEAD OF THE STRUT AND THE STABILIZER BEHIND THE STRUT. 